The invention refers to an arrangement for the detection of particles in a gas flow whereby a measuring device is provided which responds to the presence of particles. A light source is provided together with a light detector which receives the light proceeding from the light source. This light is influenced by the particles so as to control a connected evaluating circuit.
An arrangement of this sort is necessary, for example, in the case of non-mechanical fast printers with an electrophotographic printing principle. There, the residual toner, which, after the printing, is still located on the photoconductor drum, must be sucked off and caught in a paper filter (see, for example, U.S. Pat. No. 3,795,025, incorporated herein by reference). The filter must be monitored so that in the case of a defect, the printer is immediately disconnected and no toner gets into the environment of the printer with the exhaust air. Thus, an arrangement is necessary with which it can be determined whether particles are contained in the gas flow behind the filter.
An arrangement of this sort is known from German LP No. 2,654,726, incorporated herein by reference. There, a probe constructed of a light-permeable hollow body is arranged in the gas flow. In the hollow body, there is a light source which illuminates the hollow body on the side of the wall upon which the gas flow strikes and upon which particles contained in the gas flow settle. In the hollow body there is a light detector upon which the light reflected on this side of the wall strikes. The light detector releases a signal which is proportional to the reflected light intensity. This signal can then be further evaluated. A disadvantage of this arrangement is that it is not very precise.